1. Field of the Invention
The present invention relates to television signal processing and, particularly, to improving the edge transitions, i.e. shortening the rise and fall times of a video signal.
2. Description of the Prior Art
Prior means for improving the edge transitions of video signals include the addition of an enhancement or peaking signal to the original video signal. These enhancement or peaking signals are normally generated through such techniques as taking the first or second derivative of the original video signal, and adding the derivative signal, in an appropriate amount and polarity, to the original video signal. Another technique is to use a transversal filter, such as a tapped delay line; wherein, input, output and tap signals are suitably weighted, signed and combined to produce a "peaked" output signal. Still another technique is use a delay line that is unterminated on its output but terminated on its input. By subtracting the output signal from the input signal, a "peaking" signal is produced that is added in an appropriate amount and polarity to the output signal.
A U.S. Pat. No. 4,414,564 by James Hitchcock employs a non-linear technique for edge enhancement that is different from the present invention.
In order for these methods to achieve significant improvement in the resulting signals rise and fall times of edge transitions, a relatively large amount of enhancement or "peaking" signal must be added to the original video signal. However, this also produces excessive preshoots and overshoots at the edge transitions. In a television system, the white going preshoots and overshoots can cause spot blooming on the CRT display.